1. Field of the Invention
The present invention relates to cutting tools, namely toolholders for inserts for machine tools, and more particularly, to toolholders for small size inserts for grooving and turning.
2. Description of Related Art
The art of cutting grooves in a workpiece using a cutting tool, and particularly using an insert secured in a toolholder is well known. The use of an insert in a toolholder for turning, i.e., removing portions of material from a rotating workpiece by causing the insert to traverse along a portion of the longitudinal surface of the workpiece while the insert is sequentially advanced into the surface of the workpiece, is also known.
In one method of securing the insert during its use, particularly for grooving, cutting or threading, the insert is clamped adjacent one side of a toolholder. In this arrangement the toolholder has a nest or pocket formed by a bottom wall and a side wall, and the insert is held in position by a top clamp. Such an arrangement is illustrated in U.S. Pat. No. 3,754,309, issued to Jones et al. on Aug. 28, 1973.
Turning, for example in a lathe, advantageously is performed by traversing and removing material from the workpiece in both longitudinal directions. However, attempts to use the same insert within a holder for both grooving and turning, especially during turning in both directions, presents problems in securely and accurately maintaining the insert in position during these operations. In particular, during turning, and most especially upon the workpiece being traversed in the direction outwardly from that side of the holder to which the insert is clamped, the outward end of the insert held by a clamp to the toolholder tends to slip or rotate sideways due to the lateral force of the workpiece on the outward end of the insert. This is particularly the case where the bottom insert supporting surface of the holder is planar and perpendicular to the sides as in U.S. Pat. No. 3,754,309. Even where the bottom insert supporting surface of the holder is not planar, but is angled as in U.S. Pat. No. 6,000,885, issued to Erickson on Dec. 14, 1999, the insert tends to slip or rotate from the holder.
Attempts have been made to overcome the tendency of the insert to slip or rotate in the holder due to lateral force on the insert, for example by forming a diagonal notch in the insert and angling the clamp element to engage the notch and by forming recessed angled portions in the top and/or bottom surfaces of the insert, as in U.S. Pat. Nos. 3,754,309 and 6,000,885. However, such attempts have generally been imperfect to counter the force exerted on the insert as explained in U.S. Pat. No. 6,000,885. Furthermore, the attempts to date have not been applicable to small-size inserts. Small-size inserts are inserts having grooving widths in the range of from about 0.004 inch to about 0.125 inch and a body diameter of approximately 0.125 inch. Due to the small size of these inserts, it is impractical to attempt to form diagonal notches and recessed portions in the shank portion of the insert, particularly where the insert is a carbide tool insert.
In another attempt to provide a small-shank tool, and thus one or more small-size inserts, for an automatic lathe or like turning machine, a round or circular cross-sectioned elongated shank or toolholder was provided to support a pair of rhomboidal-shaped inserts, with fasteners passing through the inserts and into the toolholder to hold the inserts to the shank, as in U.S. Pat. No. 6,033,158. However, the support provided for the inserts is limited in size and orientation, i.e., the inserts extend transversely to the axis of the shank, and depend upon fasteners passing through the inserts to resist the forces encountered during cutting, grooving and turning operations. In small-size inserts it is impractical to have an aperture formed therein to receive, if it provided with cause a fastener, a weakened area, particularly if the insert is a carbide tool insert.
In still another attempt to provide inserts and toolholders which can resist the dislodging of the insert from the holder upon encountering cutting, grooving and turning forces, an insert of generally rectangular cross-section is provided with concave upper and lower clamping surfaces which cooperate with concavely-shaped clamping surfaces of a toolholder, as in U.S. Pat. No. 5,076,738. However, the generally rectangular-shaped inserts having arcuate clamping surfaces do not lend themselves for use as small-size inserts in which it would be extremely difficult to form concave upper and lower clamping surfaces, particularly where the insert is a carbide tool insert.
Thus, there exists a need for toolholders for small-sized inserts which are configured to resist forces exerted on the insert, particularly during turning.